Antimicrobial susceptibility, serotype distribution, virulence profile and molecular typing of piliated clinical isolates of pneumococci from east coast, Peninsular Malaysia

Pilus has been recently associated with pneumococcal pathogenesis in humans. The information regarding piliated isolates in Malaysia is scarce, especially in the less developed states on the east coast of Peninsular Malaysia. Therefore, we studied the characteristics of pneumococci, including the piliated isolates, in relation to antimicrobial susceptibility, serotypes, and genotypes at a major tertiary hospital on the east coast of Peninsular Malaysia. A total of 100 clinical isolates collected between September 2017 and December 2019 were subjected to serotyping, antimicrobial susceptibility test, and detection of pneumococcal virulence and pilus genes. Multilocus sequence typing (MLST) and phylogenetic analysis were performed only for piliated strains. The most frequent serotypes were 14 (17%), 6A/B (16%), 23F (12%), 19A (11%), and 19F (11%). The majority of isolates were resistant to erythromycin (42%), tetracycline (37%), and trimethoprim-sulfamethoxazole (24%). Piliated isolates occurred in a proportion of 19%; 47.3% of them were multidrug-resistant (MDR) and a majority had serotype 19F. This study showed ST236 was the most predominant sequence type (ST) among piliated isolates, which was related to PMEN clone Taiwan19F-14 (CC271). In the phylogenetic analysis, the piliated isolates were grouped into three major clades supported with 100% bootstrap values. Most piliated isolates belonged to internationally disseminated clones of S. pneumoniae, but pneumococcal conjugate vaccines (PCVs) have the potential to control them.

Species-Specific Recognition of Sulfolobales Mediated by UV-Inducible Pili and S-Layer Glycosylation Patterns

The UV-inducible pili system of Sulfolobales (Ups) mediates the formation of species-specific cellular aggregates. Within these aggregates, cells exchange DNA to repair DNA double-strand breaks via homologous recombination. Substitution of the Sulfolobus acidocaldarius pilin subunits UpsA and UpsB with their homologs from Sulfolobus tokodaii showed that these subunits facilitate species-specific aggregation. A region of low conservation within the UpsA homologs is primarily important for this specificity. Aggregation assays in the presence of different sugars showed the importance of N-glycosylation in the recognition process. In addition, the N-glycan decorating the S-layer of S. tokodaii is different from the one of S. acidocaldarius Therefore, each Sulfolobus species seems to have developed a unique UpsA binding pocket and unique N-glycan composition to ensure aggregation and, consequently, also DNA exchange with cells from only the same species, which is essential for DNA repair by homologous recombination.IMPORTANCE Type IV pili can be found on the cell surface of many archaea and bacteria where they play important roles in different processes. The UV-inducible pili system of Sulfolobales (Ups) pili from the crenarchaeal Sulfolobales species are essential in establishing species-specific mating partners, thereby assisting in genome stability. With this work, we show that different Sulfolobus species have specific regions in their Ups pili subunits, which allow them to interact only with cells from the same species. Additionally, different Sulfolobus species have unique surface-layer N-glycosylation patterns. We propose that the unique features of each species allow the recognition of specific mating partners. This knowledge for the first time gives insights into the molecular basis of archaeal self-recognition.

Animal Enterotoxigenic Escherichia coli

Enterotoxigenic Escherichia coli (ETEC) is the most common cause of E. coli diarrhea in farm animals. ETEC are characterized by the ability to produce two types of virulence factors: adhesins that promote binding to specific enterocyte receptors for intestinal colonization and enterotoxins responsible for fluid secretion. The best-characterized adhesins are expressed in the context of fimbriae, such as the F4 (also designated K88), F5 (K99), F6 (987P), F17, and F18 fimbriae. Once established in the animal small intestine, ETEC produce enterotoxin(s) that lead to diarrhea. The enterotoxins belong to two major classes: heat-labile toxins that consist of one active and five binding subunits (LT), and heat-stable toxins that are small polypeptides (STa, STb, and EAST1). This review describes the disease and pathogenesis of animal ETEC, the corresponding virulence genes and protein products of these bacteria, their regulation and targets in animal hosts, as well as mechanisms of action. Furthermore, vaccines, inhibitors, probiotics, and the identification of potential new targets by genomics are presented in the context of animal ETEC.

Application of MLST and pilus gene sequence comparisons to investigate the population structures of Actinomyces naeslundii and Actinomyces oris

Actinomyces naeslundii and Actinomyces oris are members of the oral biofilm. Their identification using 16S rRNA sequencing is problematic and better achieved by comparison of metG partial sequences. A. oris is more abundant and more frequently isolated than A. naeslundii. We used a multi-locus sequence typing approach to investigate the genotypic diversity of these species and assigned A. naeslundii (n = 37) and A. oris (n = 68) isolates to 32 and 68 sequence types (ST), respectively. Neighbor-joining and ClonalFrame dendrograms derived from the concatenated partial sequences of 7 house-keeping genes identified at least 4 significant subclusters within A. oris and 3 within A. naeslundii. The strain collection we had investigated was an under-representation of the total population since at least 3 STs composed of single strains may represent discrete clusters of strains not well represented in the collection. The integrity of these sub-clusters was supported by the sequence analysis of fimP and fimA, genes coding for the type 1 and 2 fimbriae, respectively. An A. naeslundii subcluster was identified with both fimA and fimP genes and these strains were able to bind to MUC7 and statherin while all other A. naeslundii strains possessed only fimA and did not bind to statherin. An A. oris subcluster harboured a fimA gene similar to that of Actinomyces odontolyticus but no detectable fimP failed to bind significantly to either MUC7 or statherin. These data are evidence of extensive genotypic and phenotypic diversity within the species A. oris and A. naeslundii but the status of the subclusters identified here will require genome comparisons before their phylogenic position can be unequivocally established.

Fast uncoiling kinetics of F1C pili expressed by uropathogenic Escherichia coli are revealed on a single pilus level using force-measuring optical tweezers

Uropathogenic Escherichia coli (UPEC) express various kinds of organelles, so-called pili or fimbriae, that mediate adhesion to host tissue in the urinary tract through specific receptor-adhesin interactions. The biomechanical properties of these pili have been considered important for the ability of bacteria to withstand shear forces from rinsing urine flows. Force-measuring optical tweezers have been used to characterize individual organelles of F1C type expressed by UPEC bacteria with respect to such properties. Qualitatively, the force-versus-elongation response was found to be similar to that of other types of helix-like pili expressed by UPEC, i.e., type 1, P, and S, with force-induced elongation in three regions, one of which represents the important uncoiling mechanism of the helix-like quaternary structure. Quantitatively, the steady-state uncoiling force was assessed as 26.4 ±1.4 pN, which is similar to those of other pili (which range from 21 pN for S(I) to 30 pN for type 1). The corner velocity for dynamic response (1,400 nm/s) was found to be larger than those of the other pili (400-700 nm/s for S and P pili, and 6 nm/s for type 1). The kinetics were found to be faster, with a thermal opening rate of 17 Hz, a few times higher than S and P pili, and three orders of magnitude higher than type 1. These data suggest that F1C pili are, like P and S pili, evolutionarily selected to primarily withstand the conditions expressed in the upper urinary tract.

Type-IV pili spectroscopic markers: applications in the quantification of piliation levels in Moraxella bovis cells by a FT-IR ANN-based model

Type-IV pili are cell surface organelles found in a wide variety of Gram-negative bacteria. They have traditionally been detected by electron microscopy and ELISA techniques. However, these methodologies are not appropriate for the rapid discrimination and quantification of piliated and nonpiliated cells in industrial or field conditions. Here, the analysis of FT-IR spectra of piliated, nonpiliated and sheared Moraxella bovis cells, together with purified pili suspensions spectra, allowed the identification of 3 IR regions associated to spectroscopic markers of Type-IV pili: 1750-1600, 1450-1350 and 1280-950 cm(-1). Such IR-specific markers were found for piliated cells grown in different culture systems (liquid or solid media), independently of the strain or pili serotype. They were also sensitive to pili expression levels. Therefore, on the bases of these specific spectral features, an FT-IR ANN-based model was developed to classify piliation levels in 5 distinct groups. An overall classification rate of almost 90% demonstrates the strong potential of the ANN system developed to monitor M. bovis cultures in vaccine production.

Specific involvement of pilus type 2a in biofilm formation in group B Streptococcus

Streptococcus agalactiae is the primary colonizer of the anogenital mucosa of up to 30% of healthy women and can infect newborns during delivery and cause severe sepsis and meningitis. Persistent colonization usually involves the formation of biofilm and increasing evidences indicate that in pathogenic streptococci biofilm formation is mediated by pili. Recently, we have characterized pili distribution and conservation in 289 GBS clinical isolates and we have shown that GBS has three pilus types, 1, 2a and 2b encoded by three corresponding pilus islands, and that each strain carries one or two islands. Here we have investigated the capacity of these strains to form biofilms. We have found that most of the biofilm-formers carry pilus 2a, and using insertion and deletion mutants we have confirmed that pilus type 2a, but not pilus types 1 and 2b, confers biofilm-forming phenotype. We also show that deletion of the major ancillary protein of type 2a did not impair biofilm formation while the inactivation of the other ancillary protein and of the backbone protein completely abolished this phenotype. Furthermore, antibodies raised against pilus components inhibited bacterial adherence to solid surfaces, offering new strategies to prevent GBS infection by targeting bacteria during their initial attachment to host epithelial cells.

Identification of Edwardsiella ictaluri and E. tarda by species-specific polymerase chain reaction targeted to the upstream region of the fimbrial gene

Phylogenetic analysis of nine strains of Edwardsiella ictaluri and eight strains of E. tarda (six typical motile strains and two atypical nonmotile strains) isolated from diseased fish was performed using the upstream region of the fimbrial gene cluster. Strains of E. ictaluri and E. tarda were significantly clustered into separate groups. Moreover, atypical E. tarda strains were clustered into a different group from the other strains. Three polymerase chain reaction (PCR) primer sets for differential detection of E. ictaluri as well as typical and atypical E. tarda were developed from the respective characteristic sequences. Strains of E. ictaluri, typical E. tarda, and atypical E. tarda were specifically detected by PCR using each primer set. No amplifications were observed after the use of these three primer sets with 25 other bacterial species, including fish pathogens. In addition, the three primer sets were able to detect the DNA of each target species from fish kidney and liver artificially infected with E. ictaluri or E. tarda.

Evolution of the chaperone/usher assembly pathway: fimbrial classification goes Greek

Many Proteobacteria use the chaperone/usher pathway to assemble proteinaceous filaments on the bacterial surface. These filaments can curl into fimbrial or nonfimbrial surface structures (e.g., a capsule or spore coat). This article reviews the phylogeny of operons belonging to the chaperone/usher assembly class to explore the utility of establishing a scheme for subdividing them into clades of phylogenetically related gene clusters. Based on usher amino acid sequence comparisons, our analysis shows that the chaperone/usher assembly class is subdivided into six major phylogenetic clades, which we have termed alpha-, beta-, gamma-, kappa-, pi-, and sigma-fimbriae. Members of each clade share related operon structures and encode fimbrial subunits with similar protein domains. The proposed classification system offers a simple and convenient method for assigning newly discovered chaperone/usher systems to one of the six major phylogenetic groups.

Type III secretion system-associated pilus of Pseudomonas syringae as an epitope display tool

Type III secretion system-associated pili found in several plant pathogenic bacteria are required for injection of virulence proteins from bacteria into the plant cells. The possibility to use the type III secretion pilus of Pseudomonas syringae as an epitope display tool was studied. The advantage of the type III secretion pilus, compared with conventional fimbrial epitope display tools, is that the pilin subunits of the type III secretion pilus can auto-assemble into intact pili in vitro. Various peptides were inserted into the type III secretion pilin subunit, and secretion, assembly and surface properties of the modified pili were monitored. It was concluded that the outwards-projecting N-terminal region of the pilin can bear even 43 amino acids insertion. The three-dimensional structure of the epitope, however, can restrict the use of the pilus as an epitope display tool: a beta-hairpin structure was poorly tolerated.

Characterization of adhesin variants in Indian isolates of enteroaggregativeEscherichia coli

Enteroaggregative Escherichia coli (EAEC) are causative agents of diarrhea, being characterized by aggregative adherence to cultured epithelial cells. In this study, phenotypic properties of EAEC were analyzed with respect to AA, hemagglutination, clump and biofilm formation, all of which are mediated by aggregative adherence fimbriae (AAF). The strains were also screened for AAF types, AAF adhesin variants and Dr adhesin by PCR. Of the three known AAF types, AAF/I and AAF/II adhesin variants were identified. An association between the AAF/adhesin genotypes and the subtypes/scores of phenotypic properties was sought and it was observed that strains harboring same adhesins displayed different subtypes/scores and vice versa.

Aptamers that preferentially bind type IVB pili and inhibit human monocytic-cell invasion by Salmonella enterica serovar typhi

Salmonella enterica serovar Typhi is an important pathogen exclusively for humans and causes typhoid or enteric fever. It has been shown that type IVB pili, encoded by the S. enterica serovar Typhi pil operon located in Salmonella pathogenicity island 7, are important in the pathogenic process. In this study, by using both an adhesion-invasion assay and fluorescence quantitative PCR analysis, we demonstrated that the entry of type IVB piliated S. enterica serovar Typhi A21-6 (pil(+) Km(r)) into human THP-1 monocytic cells was greater than that of a nonpiliated S. enterica serovar Typhi pilS::Km(r) (pil mutant) strain. We have applied a systematic evolution of ligands by exponential enrichment approach to select oligonucleotides (aptamers) as ligands that specifically bind to type IVB pili. Using this approach, we identified a high-affinity single-stranded RNA aptamer (S-PS(8.4)) as a type IVB pilus-specific ligand and further found that the selected aptamer (S-PS(8.4)) could significantly inhibit the entry of the piliated strain (but not that of the nonpiliated strain) into human THP-1 cells. The binding affinities between aptamers and pre-PilS (structural protein of type IVB pili) were determined by nitrocellulose filter-binding assays, and the K(d) value was determined to be 8.56 nM for the S-PS(8.4) aptamer alone. As an example of an aptamer against type IVB pili of S. enterica serovar Typhi, the aptamer S-PS(8.4) can serve as a tool for analysis of bacterial type IVB pilus-host cell interactions and may yield information for the development of putative new drugs against S. enterica serovar Typhi bacterial infections, useful both in prevention of infection and in therapeutic treatment.

The Distinct Binding Specificities Exhibited by Enterobacterial Type 1 Fimbriae Are Determined by Their Fimbrial Shafts

Type 1 fimbriae of enterobacteria are heteropolymeric organelles of adhesion composed of FimH, a mannose-binding lectin, and a shaft composed primarily of FimA. We compared the binding activities of recombinant clones expressing type 1 fimbriae from Escherichia coli, Klebsiella pneumoniae, and Salmonella typhimurium for gut and uroepithelial cells and for various soluble mannosylated proteins. Each fimbria was characterized by its capacity to bind particular epithelial cells and to aggregate mannoproteins. However, when each respective FimH subunit was cloned and expressed in the absence of its shaft as a fusion protein with MalE, each FimH bound a wide range of mannose-containing compounds. In addition, we found that expression of FimH on a heterologous fimbrial shaft, e.g. K. pneumoniae FimH on the E. coli fimbrial shaft or vice versa, altered the binding specificity of FimH such that it closely resembled that of the native heterologous type 1 fimbriae. Furthermore, attachment to and invasion of bladder epithelial cells, which were mediated much better by native E. coli type 1 fimbriae compared with native K. pneumoniae type 1 fimbriae, were found to be dependent on the background of the fimbrial shaft (E. coli versus K. pneumoniae) rather than the background of the FimH expressed. Thus, the distinct binding specificities of different enterobacterial type 1 fimbriae cannot be ascribed solely to the primary structure of their respective FimH subunits, but are also modulated by the fimbrial shaft on which each FimH subunit is presented, possibly through conformational constraints imposed on FimH by the fimbrial shaft. The capacity of type 1 fimbrial shafts to modulate the tissue tropism of different enterobacterial species represents a novel function for these highly organized structures.

Evolutionary and functional relationships of colonization factor antigen i and other class 5 adhesive fimbriae of enterotoxigenic Escherichia coli

Colonization factor antigen I (CFA/I) is the archetype of eight genetically related fimbriae of enterotoxigenic Escherichia coli (ETEC) designated class 5 fimbriae. Assembled by the alternate chaperone pathway, these organelles comprise a rigid stalk of polymerized major subunits and an apparently tip-localized minor adhesive subunit. We examined the evolutionary relationships of class 5-specific structural proteins and correlated these with functional properties. We sequenced the gene clusters encoding coli surface antigen 4 (CS4), CS14, CS17, CS19, and putative colonization factor antigen O71 (PCFO71) and analyzed the deduced proteins and the published homologs of CFA/I, CS1, and CS2. Multiple alignment and phylogenetic analysis of the proteins encoded by each operon define three subclasses, 5a (CFA/I, CS4, and CS14), 5b (CS1, CS17, CS19, and PCFO71), and 5c (CS2). These share distant evolutionary relatedness to fimbrial systems of three other genera. Subclass divisions generally correlate with distinguishing in vitro adherence phenotypes of strains bearing the ETEC fimbriae. Phylogenetic comparisons of the individual structural proteins demonstrated greater intrasubclass conservation among the minor subunits than the major subunits. To correlate this with functional attributes, we made antibodies against CFA/I and CS17 whole fimbriae and maltose-binding protein fusions with the amino-terminal half of the corresponding minor subunits. Anti-minor subunit Fab preparations showed hemagglutination inhibition (HAI) of ETEC expressing homologous and intrasubclass heterologous colonization factors while anti-fimbrial Fab fractions showed HAI activity limited to colonization factor-homologous ETEC. These results were corroborated with similar results from the Caco-2 cell adherence assay. Our findings suggest that the minor subunits of class 5 fimbriae may be superior to whole fimbriae in inducing antiadhesive immunity.

Variations of Porphyromonas gingivalis fimbriae in relation to microbial pathogenesis

OBJECTIVES

Periodontal disease is an infectious disorder caused by a small subset of periodontal pathogens including Porphyromonas gingivalis. Accumulated evidences show that the expression of P. gingivalis heterogenic virulence properties is dependent on its clonal diversity. P. gingivalis expresses two distinct fimbria molecules, major and minor fimbriae, on its cell surfaces, both of which seem to be involved in the development of periodontitis. In this short review, variations of fimbriae in relation to microbial pathogenesis are discussed.

MATERIALS AND METHODS

Our recent findings are summarized to elucidate the relationship between clonal variation of fimbriae and bacterial pathogenicity of various strains.

RESULTS

Major fimbriae were classified into six types (I to V and Ib) based on the diversity of fimA genes encoding FimA (a subunit of major fimbriae). A majority of periodontitis patients were found to carry type II fimA organisms, followed by type IV, and type II fimA organisms were significantly occurred with more severe forms of periodontitis. Studies of clones with type II fimA have revealed significantly greater adhesive and invasive capabilities to epithelial cells than other fimA type clones. Minor fimbriae induced interleukin-1alpha (IL-1alpha), IL-1beta, IL-6, and tumor necrosis factor-alpha (TNF-alpha) cytokine expression in macrophages and were suggested to be a causative factor of alveolar bone resorption in animal models. The clonal diversity of minor fimbriae is unclear, however, distinct minor fimbria molecules were found in different strains.

CONCLUSION

The fimbria variations may have an influence on the development of periodontal disease.

The type IVB pili of Salmonella enterica serovar Typhi bind to the cystic fibrosis transmembrane conductance regulator

Salmonella enterica serovar Typhi expresses type IVB pili. We show that the prePilS protein (the soluble precursor form of the structural pilin) interacts with a 15-mer peptide representing the first extracellular domain of the cystic fibrosis transmembrane conductance regulator (CFTR), a recognized human epithelial cell receptor for serovar Typhi (G. B. Pier et al., Nature 393:79-82, 1998). This indicates that after mediating bacterial self-association (C. Morris et al., Infect. Immun. 71:1141-1146, 2003), the pili then act to attach the bacterial clumps to CFTR in the membrane of gut epithelial cells. These sequential type IVB pilus-mediated events cannot be performed by (for example) S. enterica serovar Typhimurium, which may explain why only serovar Typhi causes epidemics of enteric fever in humans.

Exploring the 3D molecular architecture of Escherichia coli type 1 pili

An integrated approach combining information gained by Fourier transformation, linear Markham superposition (real space) and mass-per-length measurement by scanning transmission electron microscopy was used to analyze the helical structure of the rod-like type 1 pili expressed by uropathogenic Escherichia coli strain W3110. The 3D reconstruction calculated from the experimental data showed the pili to be 6.9nm wide, right-handed helical tubes with a 19.31(+/-0.34)nm long helical repeat comprising 27 FimA monomers associated head-to-tail in eight turns of the genetic one-start helix. Adjacent turns of the genetic helix are connected via three binding sites making the pilus rod rather stiff. In situ immuno-electron microscopy experiments showed the minor subunit (FimH) mediating pilus adhesion to bladder epithelial cells to be the distal protein of the pilus tip, which had a spring-like appearance at higher magnification. The subunits FimG and FimF connect FimH to the FimA rod, the sequential orientation being FimA-FimF-FimG-FimH. The electron density map calculated at 18A resolution from an atomic model of the pilus rod (built using the pilin domain FimH together with the G1 strand of FimC as a template for FimA and applying the optimal helical parameters determined to the head-to-tail interaction model for pilus assembly) was practically identical with that of the actual 3D reconstruction.

Cytokine production induced by a 67-kDa fimbrial protein from Porphyromonas gingivalis

Fimbriae have been reported to play an important role in the adherence of Porphyromonas gingivalis to oral surfaces and possibly in triggering host responses. P. gingivalis ATCC 33277 has two distinctly different fimbriae expressed on the cell surface. The 67-kDa fimbriae differ in size and antigenicity from the earlier reported FimA, a major 41-kDa fimbrial component of P. gingivalis. Expression of the 67-kDa fimbriae on the cell surface of a fimA mutant was investigated by electron microscopy. The 67-kDa fimbrial protein was purified from the fimA mutant by sonication, precipitation, and chromatography on a DEAE Sepharose CL-6B column. The N-terminal amino acid sequence of the 67-kDa fimbrillin was distinct from that of the 41-kDa fimbrillin. Moreover, we have found that the 67-kDa fimbrial protein from P. gingivalis ATCC 33277 induced IL-1alpha, IL-beta, IL-6 and TNFalpha cytokine expression in mouse peritoneal macrophages. These results suggest that P. gingivalis 67-kDa fimbriae may play a part in the inflammatory response during the development of periodontal diseases.

Different type 1 fimbrial genes and tropisms of commensal and potentially pathogenic Actinomyces spp. with different salivary acidic proline-rich protein and statherin ligand specificities

Actinomyces spp. exhibit type 1 fimbria-mediated adhesion to salivary acidic proline-rich proteins (PRPs) and statherin ligands. Actinomyces spp. with different animal and tissue origins belong to three major adhesion types as relates to ligand specificity and type 1 fimbria genes. (i) In preferential acidic-PRP binding, strains of Actinomyces naeslundii genospecies 1 and 2 from human and monkey mouths displayed at least three ligand specificities characterized by preferential acidic-PRP binding. Slot blot DNA hybridization showed seven highly conserved type 1 fimbria genes (orf1- to -6 and fimP) in genospecies 1 and 2 strains, except that orf5 and orf3 were divergent in genospecies 1. (ii) In preferential statherin binding, oral Actinomyces viscosus strains of rat and hamster origin (and strain 19246 from a human case of actinomycosis) bound statherin preferentially. DNA hybridization and characterization of the type 1 fimbria genes from strain 19246 revealed a homologous gene cluster of four open reading frames (orfA to -C and fimP). Bioinformatics suggested sortase (orfB, orf4, and part of orf5), prepilin peptidase (orfC and orf6), fimbria subunit (fimP), and usher- and autotransporter-like (orfA and orf1 to -3) functions. Those gene regions corresponding to orf3 and orf5 were divergent, those corresponding to orf2, orf1, and fimP were moderately conserved, and those corresponding to orf4 and orf6 were highly conserved. Restriction fragment length polymorphism analyses using a fimP probe separated human and monkey and rat and hamster strains into phylogenetically different groups. (iii) In statherin-specific binding, strains of A. naeslundii genospecies 1 from septic and other human infections displayed a low-avidity binding to statherin. Only the orf4 and orf6 gene regions were highly conserved. Finally, rat saliva devoid of statherin bound bacterial strains avidly irrespective of ligand specificity, and specific antisera detected either type 1, type 2, or both types of fimbria on the investigated Actinomyces strains.

A novel interaction between type IV pili of Neisseria gonorrhoeae and the human complement regulator C4B-binding protein

C4b-binding protein (C4BP) is an important plasma inhibitor of the classical pathway of complement activation. Several bacterial pathogens bind C4BP, which may contribute to their virulence. In the present report we demonstrate that isolated type IV pili from Neisseria gonorrhoeae bind human C4BP in a dose-dependent and saturable manner. C4BP consists of seven identical alpha-chains and one beta-chain linked together with disulfide bridges. We found that pili bind to the alpha-chain of C4BP, which is composed of eight homologous complement control protein (CCP) domains. From the results of an inhibition assay with C4b and a competition assay in which we tested mutants of C4BP lacking individual CCPs, we concluded that the binding area for pili is localized to CCP1 and CCP2 of the alpha-chain. The binding between pili and C4BP was abolished at 0.25 M NaCl, implying that it is based mostly on ionic interactions, similarly to what have been observed for C4b-C4BP binding. Furthermore, the N-terminal part of PilC, a structural component of pili, appeared to be responsible for binding of C4BP. Membrane cofactor protein, previously shown to be a receptor for pathogenic N. gonorrhoeae on the surface of epithelial cells, competed with C4BP for binding to pili only at high concentrations, suggesting that different parts of pili are involved in these two interactions. Accordingly, high concentrations of C4BP were required to inhibit binding of N. gonorrhoeae to Chang conjunctiva cells, and no inhibition of binding was observed with cervical epithelial cells.

Identification of type 4 fimbriae in Actinobacillus pleuropneumoniae

Type 4 fimbriae have been identified on the cell surface of Actinobacillus pleuropneumoniae by electron microscopy and N-terminal sequencing analysis. A. pleuropneumoniae type 4 fimbrial subunit protein, purified from cell cultures and from outer membrane preparations, reacted with polyclonal antibody raised against type 4 fimbriae of Moraxella bovis on Western blots. N-terminal sequence analysis of the purified 17 kDa type 4 fimbrial subunit protein, named ApfA, revealed the first 12 amino acids to be identical to those of other type 4 fimbrial subunit proteins.

Identification of the F17 fimbrial subunit- and adhesin-encoding (f17A and f17G) gene variants in necrotoxigenic Escherichia coli from cattle, pigs and humans

Putative colonization factors of the F17 family of fimbrial adhesins have been identified in necrotoxigenic Escherichia coli Type 1 and Type 2 (NTEC1 and NTEC2) from calves, pigs, and humans. The f17A and f17G gene variants, coding respectively for the major subunit and for the adhesin of the F17 fimbriae, were typed in 70 E. coli carrying f17-related sequences (15 NTEC1, 51 NTEC2, and four non-NTEC) by colony hybridisation with gene probes derived from the different f17A gene variants (a, b, c, and d) and by PCRs specific for each f17A and f17G (I and II) gene variants. Typing of f17A genes was not possible by colony hybridisation, as most 70 E. coli were positive with more than one gene probe. On the other hand, the PCRs allowed the typing of the f17A gene in 37 E. coli and of the f17G gene in all 70 E. coli. The f17Ab gene variant was detected in 13 NTEC2; the f17Ac, in all 15 NTEC1, six NTEC2 and two non-NTEC; and the f17Ad, in one non-NTEC. Seven additional NTEC2 were positive with the PCRs for two variants: f17Ab and f17Ac in three of them; f17Ac and f17Ad in four of them. Either these seven NTEC2 harbour two variants or the variant present can be detected by two PCRs. The remaining 25 NTEC2 and one non-NTEC tested negative with the PCRs for the four f17A gene variants, suggesting the existence of other variant(s). In contrast, all 70 E. coli were positive with the PCR for the f17GII gene variant and none with the PCR for the f17GI gene variant. The f17-related sequences were present on the CNF2/Vir plasmids in 27 out of the 46 NTEC2 from which plasmid DNA could be extracted: all but one of those positive for the f17Ab gene variant and various proportions of those positive for other variants. In contrast, no plasmid carried f17-related sequences in NTEC1 and non-NTEC.

The F4 fimbrial antigen of Escherichia coli and its receptors

F4 or K88 fimbriae are long filamentous polymeric surface proteins of enterotoxigenic Escherichia coli (ETEC), consisting of so-called major (FaeG) and minor (FaeF, FaeH, FaeC, and probably FaeI) subunits. Several serotypes of F4 have been described, namely F4ab, F4ac, and F4ad. The F4 fimbriae allow the microorganisms to adhere to F4-specific receptors present on brush borders of villous enterocytes and consequently to colonize the small intestine. Such ETEC infections are responsible for diarrhea and mortality in neonatal and recently weaned pigs. In this review emphasis is put on the morphology, genetic configuration, and biosynthesis of F4 fimbriae. Furthermore, the localization of the different a, b, c, and d epitopes, and the localization of the receptor binding site on the FaeG major subunit of F4 get ample attention. Subsequently, the F4-specific receptors are discussed. When the three variants of F4 (F4ab, F4ac, and F4ad) are considered, six porcine phenotypes can be distinguished with regard to the brush border adhesiveness: phenotype A binds all three variants, phenotype B binds F4ab and F4ac, phenotype C binds F4ab and F4ad, phenotype D binds F4ad, phenotype E binds none of the variants, and phenotype F binds F4ab. The following receptor model is described: receptor bcd is found in phenotype A pigs, receptor bc is found in phenotype A and B pigs, receptor d is found in phenotype C and D pigs, and receptor b is found in phenotype F pigs. Furthermore, the characterization of the different receptors is described in which the bcd receptor is proposed as collection of glycoproteins with molecular masses ranging from 45 to 70 kDa, the bc receptor as two glycoproteins with molecular masses of 210 an 240 kDa, respectively, the b receptor as a glycoprotein of 74 kDa, and the d receptor as a glycosphingolipid with unknown molecular mass. Finally, the importance of F4 fimbriae and their receptors in the study of mucosal immunity in pigs is discussed.

Genotypic prevalence of F4 variants (ab, ac, and ad) in Escherichia coli isolated from diarrheic piglets in Korea

A total of 812 Escherichia coli strains isolated from diarrheic piglets were tested for the presence of the F4 (K88) variant (ab, ac and ad) gene by the polymerase chain reaction. Forty four (5.4%) of the 812 E. coli strains carried genes for F4. Among the 44 isolates known to carry genes for F4, 42 (96%) isolates contained genes for F4ac and 2 (4%) isolates contained genes for F4ab. None of the E. coli strains carried genes for F4ad. Our data show that F4ac is the predominant F4 variant associated with diarrhea in piglets in Korea.

A study of relationships among F17 a producing enterotoxigenic and non-enterotoxigenic Escherichia coli strains isolated from diarrheic calves

We investigated the clonal relationships among 41 enterotoxigenic (ETEC) or non-enterotoxigenic (NETEC) Escherichia coli strains producing the F17 a fimbriae isolated from diarrheic calves in France or Belgium in the early 1980s. Twenty-three of the 26 ETEC strains were highly clonally related, most of them with a O101:K32:H9-serotype. The NETEC strains were also divided in clonal subgroups, most of them with O101:H-serotype. The F17 a positive ETEC strains are no longer isolated from diarrheic calves in these countries. It is postulated that the use of a vaccine including O101, K32 and H9 antigens in addition to K99 (F5) explains the strongly reduced isolation of the O101:K32:H9, K99 (F5) E. coli clone.